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.TH MSYNC 3C "Jul 24, 2002"
.SH NAME
msync \- synchronize memory with physical storage
.SH SYNOPSIS
.LP
.nf
#include <sys/mman.h>

\fBint\fR \fBmsync\fR(\fBvoid *\fR\fIaddr\fR, \fBsize_t\fR \fIlen\fR, \fBint\fR \fIflags\fR);
.fi

.SH DESCRIPTION
.sp
.LP
The  \fBmsync()\fR function writes all modified copies of pages over the range
[\fIaddr, addr + len\fR) to the underlying hardware, or invalidates any copies
so that further references to the pages will be obtained by the system from
their permanent storage locations. The permanent storage for a modified
\fBMAP_SHARED\fR mapping is the file the page is mapped to; the permanent
storage for a modified \fBMAP_PRIVATE\fR mapping is its swap area.
.sp
.LP
The \fIflags\fR argument is a bit pattern built from the following values:
.sp
.ne 2
.na
\fBMS_ASYNC\fR
.ad
.RS 17n
perform asynchronous writes
.RE

.sp
.ne 2
.na
\fBMS_SYNC\fR
.ad
.RS 17n
perform synchronous writes
.RE

.sp
.ne 2
.na
\fBMS_INVALIDATE\fR
.ad
.RS 17n
invalidate mappings
.RE

.sp
.LP
If \fIflags\fR is \fBMS_ASYNC\fR or \fBMS_SYNC\fR, the function synchronizes
the file contents to match the current contents of the memory region.
.RS +4
.TP
.ie t \(bu
.el o
All write references to the memory region made prior to the call are visible by
subsequent read operations on the file.
.RE
.RS +4
.TP
.ie t \(bu
.el o
All writes to the same portion of the file prior to the call may or may not be
visible by read references to the memory region.
.RE
.RS +4
.TP
.ie t \(bu
.el o
Unmodified pages in the specified range are not written to the underlying
hardware.
.RE
.sp
.LP
If \fIflags\fR is \fBMS_ASYNC\fR, the function may return immediately once all
write operations are scheduled; if \fIflags\fR is \fBMS_SYNC\fR, the function
does not return until all write operations are completed.
.sp
.LP
If \fIflags\fR is \fBMS_INVALIDATE\fR, the function synchronizes the contents
of the memory region to match the current file contents.
.RS +4
.TP
.ie t \(bu
.el o
All writes to the mapped portion of the file made prior to the call are visible
by subsequent read references to the mapped memory region.
.RE
.RS +4
.TP
.ie t \(bu
.el o
All write references prior to the call, by any process, to memory regions
mapped to the same portion of the file using \fBMAP_SHARED\fR, are visible by
read references to the region.
.RE
.sp
.LP
If \fBmsync()\fR causes any write to the file, then the file's \fBst_ctime\fR
and \fBst_mtime\fR fields are marked for update.
.SH RETURN VALUES
.sp
.LP
Upon successful completion, \fBmsync()\fR returns \fB0\fR; otherwise, it
returns \fB\(mi1\fR and sets \fBerrno\fR to indicate the error.
.SH ERRORS
.sp
.LP
The \fBmsync()\fR function will fail if:
.sp
.ne 2
.na
\fB\fBEBUSY\fR\fR
.ad
.RS 10n
Some or all of the addresses in the range [\fIaddr\fR, \fIaddr\fR + \fIlen\fR)
are locked and \fBMS_SYNC\fR with the \fBMS_INVALIDATE\fR option is specified.
.RE

.sp
.ne 2
.na
\fB\fBEAGAIN\fR\fR
.ad
.RS 10n
Some or all pages in the range [\fIaddr\fR,  \fIaddr\fR +  \fIlen\fR) are
locked for I/O.
.RE

.sp
.ne 2
.na
\fB\fBEINVAL\fR\fR
.ad
.RS 10n
The \fIaddr\fR argument is not a multiple of the  page size as returned by
\fBsysconf\fR(3C).
.sp
The \fIflags\fR argument is not some combination of \fBMS_ASYNC\fR and
\fBMS_INVALIDATE\fR.
.RE

.sp
.ne 2
.na
\fB\fBEIO\fR\fR
.ad
.RS 10n
An I/O error occurred while reading from or writing to the file system.
.RE

.sp
.ne 2
.na
\fB\fBENOMEM\fR\fR
.ad
.RS 10n
Addresses in the range [\fIaddr, addr + len\fR) are outside the valid range for
the address space of a process, or specify one or more pages that are not
mapped.
.RE

.sp
.ne 2
.na
\fB\fBEPERM\fR\fR
.ad
.RS 10n
\fBMS_INVALIDATE\fR was specified and one or more of the pages is locked in
memory.
.RE

.SH USAGE
.sp
.LP
The \fBmsync()\fR function should be used by programs that require a memory
object to be in a known state, for example in building transaction facilities.
.sp
.LP
Normal system activity can cause pages to be written to disk.  Therefore, there
are no guarantees that \fBmsync()\fR is the only control over when pages are or
are not written to disk.
.SH ATTRIBUTES
.sp
.LP
See \fBattributes\fR(7) for descriptions of the following attributes:
.sp

.sp
.TS
box;
c | c
l | l .
ATTRIBUTE TYPE	ATTRIBUTE VALUE
_
Interface Stability	Standard
_
MT-Level	MT-Safe
.TE

.SH SEE ALSO
.sp
.LP
.BR memcntl (2),
.BR mmap (2),
.BR sysconf (3C),
.BR attributes (7),
.BR standards (7)
